The increasing demand for transportation fuel has necessitated the need for processing the heavier residues containing higher contents of asphaltenes. Asphaltenes are considered to be the most troublesome fractions in petroleum cracking and refining. Because of their condensed structure, asphaltenes tend to be extremely refractory during processing operations and cause serious problems in resid processing such as hydrocracking and hydrodesulphurization. Therefore, attempt is made to understand the changes in asphaltenes structure during processing and collected vital information needed to upgrade the technology for refining heavy oils and residues containing a substantial portion of asphaltenes. Hydrotreatment reactions were performed on atmospheric residue using different catalysts and AIBN free radical initiator. Structural characterization of asphaltenes isolated from Arabian heavy residue was undertaken. The analyses indicated the cracking of larger molecules took place. The compositional data generated by this work will enhance the understanding of asphaltenes and help in improving refining practices and geochemical studies.